The invention relates to an apparatus for mixing a solution of concentrates, particularly of water and liquid polymers. Such aqueous solutions are useful for many applications including the tertiary recovery of petroleum from a subterranean reservoir to enhance production of the latter. Said mixing apparatus comprises primarily a metering chamber into which flowing water, and a flowing concentrate, are brought together in controlled amounts to be mixed.
Polymers, particularly for the tertiary recovery of crude oil from a well or bore, are for example copolymers of acrylamide and sodium acrylate, polyacrylamideacrylates, hereinafter referred to as PAA. As so-called emulsion polymers, such materials comprise for example a high-concentration aqueous solution, which is emulsified in petroleum in the form of small gel particles. The latter usually have a size of 1 to 2 m. Depending on the manufacturer, the proportions of the individual chemicals within a mixture are about 25% to 35% of PAA, 30% to 35% of water, and 30% to 50% of petroleum. A small amount of an emulsion-stabilizing surface-active material can also be included in the mixture.
In the tertiary recovery of crude oil from a well or subterranean reservoir, the PAA with a molecular weight of 3 to 10 millions are added to the injection water at a concentration of normally 0.3 to 1 kg/m.sup.3 of water. For such application it is essential that the polymer solution resulting from the mixing of the PAA emulsion with water, be completely free of undissolved or gel-like particles. The presence of particulate matter in the polymer solution could permanently clog the well face or the formation and would thus, over an extended period of time, inhibit injection of the polymer solution.
With respect to the usual preparation of readily injectable solutions, i.e. solutions free of obstructing gel particles, the moment of initial contact between the polymer emulsion and the water is particularly critical. If the emulsion is brought into contact with the water without special precautionary measures, the emulsion will slowly break from oil external to water external.
The gel particles thus suspended in the petroleum will stick together and form large aggregates with a high local polymer concentration. Once such aggregates have formed it is virtually impossible to redissolve them. Even if they are treated for several days by strong agitation they resist being dissolved. Such a solution therefore cannot be injected into a well.
In field operations, actual preparation of a polymer solution for injection into the substrate about a well is usually achieved by metering the liquid polymer into a rapidly flowing stream of water. This form of preparation is realized however only by accepting a number of concurrent disadvantages including the following:
1. The optimum flow rate of the flood water, and the optimum geometrical arrangement of the polymer metering location, are not accurately obtained.
2. It is frequently necessary, depending on the character of the subterranean formation, to vary injection rates in the course of a project. This could result in polymer solutions that are difficult to inject.
3. Towards the termination of the polymer injection stage it is usual to perform a step-wise reduction in the polymer solution concentration. Experience has shown that in such an instance the polymer solution will become less amenable to being injected.
It is an object of the invention therefore to provide an apparatus which fosters the preparation of an aqueous polymer solution which is characterized by its ability to be readily injectable into a substrate to enhance tertiary recovery from the latter. A further object is to provide an apparatus for mixing a plurality of elements to form a substantially homogenous solution.
In accordance with the invention the above-specified objects are achieved through use of an apparatus as hereinafter described. Said apparatus comprises in brief an elongated body having a main passage which operably receives a plunger or piston. The body includes means to receive a stream of a first liquid such as water into the main passage. The plunger includes means to controllably inject a flow of a second fluid such as the above mentioned PAA into said main passage whereby the two injected fluids will be thoroughly mixed.
A turbulence chamber formed in said main passage further enhances homogenization of the respective liquids into a uniform usable composition.
A metering head formed at the plunger inner end is spaced from contiguous walls of the body main passage to define a constricted, annular mixing compartment. Said metering head is provided with a distribution space or chamber in which a flow check valve means is positioned. A plurality of egress ports formed in the periphery of said distribution chamber, cause liquid to be injected laterally from the chamber and into the rapidly flowing stream of liquid in the constricted annular mixing compartment.
The disclosed apparatus offers the physical advantage that initially formed polymer solution will be subjected to strong turbulent action immediately after the PAA has been intermixed with the water stream in the mixing compartment. In such manner, each polymer gel particle will be individually wetted by the water and thus dissolved. The formation of larger aggregates with a high polymer concentration will thereby be prevented.
A further feature of the invention is illustrated by the size of the annular mixing compartment passage through which the water flow is passed. Said passage is reduced in cross-section normal to the liquid flow, downstream of the point where polymer fluid is added to the water flow. Preferably, this abrupt reduction in flow passage size is provided by the metering head terminating downstream of the PAA flow egress ports. Advantageously, the end of the metering head is chamfered to assure an area of turbulence.
A relatively high fluid flow rate is achieved in the region of the mixing compartment egress ports due to the constricted annular cross-section at this point. This flow rate is thereafter drastically reduced at a point immediately downstream of the metering head. The arrangement will result in establishment of a strong turbulence area, and a further homogenization of the polymer solution.
A further feature of the invention resides in the diameter of the turbulence compartment outer wall which gradually decreases at a uniform rate from approximately the region of the egress ports. As a result of the decrease in diameter, the flow rate of homogenized polymer solution will again be increased prior to being discharged through the apparatus outlet port.
In another feature of the invention the polymer concentrate supply passages extend axially through the plunger. The latter is longitudinally adjustable in the body to thereby permit the cross-section of the mixing compartment to be rapidly altered as needed.